1. Field of the Invention
The present invention relates generally to electrical devices that utilize a timing trigger to synchronize an input signal or set of signals. Specific examples of such devices are utilized in systems such as PICA, which involve the detection of optical signals generated by Integrated Circuit devices. However, the invention is not limited to this specific class of devices.
2. Background Art
The present implementation of many detection schemes, including optical signal detection schemes such as PICA, assume the use of a single timing reference source, or trigger. In a PICA detection scheme, as an example, incoming photons are converted to an electrical signal utilizing an appropriate detector. Timing measurements of the electrical signals are made by synchronization with respect to the trigger. Since the trigger typically recurs many times per second, these timing measurements are accumulated or averaged with respect to this trigger.
The scheme described above results in the gradual improvement of signal-to-noise ratio, as the results from increasing numbers of events or triggers are accumulated. This is because the desired measurement is by design synchronized with the trigger, and hence random events such as thermally generated noise will tend to “average out” or diminish to approximately a background level, while the desired signal will be reinforced, eventually becoming detectable with some precision. Not only will random noise be “averaged out,” in fact, an often desirable attribute of this scheme is that nonrandom frequency components of the signal or noise that are not synchronized with the trigger will also be attenuated.
However, in some cases it is desirable to have the ability to detect signal components that are “out of sync” with the trigger. For example, in some implementations of PICA, optical signals are detected from an area that may include many independent devices. It is possible that some of these devices may be switching at one frequency or set of frequencies, while other devices switch at a different, asynchronous frequency. In that case, the timing signal from devices that switch at frequencies asynchronous to the clock will be lost or attenuated. In order to capture the desired, asynchronous signal, the measurement must be repeated, this time using a different trigger that is synchronized with the desired time pattern. In cases where three independent frequencies are present, the measurement could be repeated three times, etc.
There is, therefore, a need in the prior art for a system which can simultaneously capture timing information with respect to two or more triggers, eliminating the need to make multiple measurements in order to detect the presence or absence of the relevant frequency components.